1. Field of the Invention
The present invention relates to a ball grid array (BGA) integrated circuit package.
2. Description of Related Art
Integrated circuits are typically assembled to a package that is mounted to a printed circuit board. There are many types of integrated circuit packages such as pin grid array (PGA), land grid array (LGA) and ball grid array (BGA). BGA packages contain a plurality of solder balls that are attached to corresponding solder pads located on an external bottom surface of the package. The package is mounted to a printed circuit board and the solder balls are reflowed to attach the package to the board.
FIG. 1 shows a solder pad layout for a BGA package of the prior art. The package includes a number of solder pads 1 located on a bottom surface of a package substrate 2. A number of routing traces 3 may also extend across the bottom surface. The routing traces 3 and portions of the solder pads 1 may be covered with a solder mask 4. The solder mask 4 has openings 5 that exposes contact areas 6 of the solder pads 1. Solder balls (not shown) are attached to the exposed contact areas 6 of the solder pads 1. The solder balls are used to mount the package to a printed circuit board. The solder mask 4 controls the diameter of the attached solder balls and prevents electrical shorts in the package.
Some of the routing traces 3 are connected to the solder pads 1. The solder pads 1 may also be connected to vias 7 that extend through the substrate 2 of the package. The circular shape of the solder pads 1 create stress points 8 at the intersection of the trace 3 and the pad 1. Stress points are also created at the intersections of the via 7, the trace 3 and the solder pad 1. Thermal cycling of the package may induce cracking at the stress points 8 of the substrate 2. Cracks may create an open circuit in the package. It would be desirable to provide a BGA package which has a more robust interconnect between the solder pads, routing traces and vias of the package.